In a wireless communications system, after being powered on, user equipment (UE) selects a suitable cell to camp on, then establishes a connection to a base station of the cell by performing a random access process, and performs a registration process, a location update process, and other processes.
After camping on a cell, the UE selects, according to changes of a location after movement, a base station of a cell, and a service and the like, a better serving cell to camp on by means of cell reselection, for example, a serving cell having better signal quality or a higher priority.
In practical application, due to a geographical environment, weather, or the like, it occurs that a base station located far from a UE can provide, a better downlink signal than a base station located near the UE, but cannot normally receive an uplink signal that is sent by the user equipment during random access, which causes that when selecting a cell to camp on, the UE selects a cell in which the base station located far from the UE is located, and the random access performed by the UE fails, leading to interruption of a service provided to the UE. Because this special situation occurs in the Chiba region in Japan, such a cell is referred to as a Chiba (CHIBA) cell. FIG. 1 is a schematic diagram of a Chiba cell in the prior art. As shown in FIG. 1, due to a reflection action of the surface of a lake, a UE receives a downlink signal of a cell A on the right of the lake better than a downlink signal of a cell B on the left of the lake, and therefore the UE selects the cell A to camp on. However, because the UE is located far from the cell A, a failure occurs when the UE initiates random access; and even though the UE successfully performs random access to the cell B, the UE still reselects the cell A due to a better downlink signal of the cell A, causing service interruption.